Casting assembly for stator coils

ABSTRACT

The terminal portion of a winding end turn conductor which projects from the core member of a dynamoelectric machine is encapsulated in an epoxy potting compound by means of a casting assembly which comprises a detachable conformable pad, a plastic sleeve mold, and a portable vise. The conformable pad is fitted about the terminal portion of the conductor to provide a temporary barrier to axial flow of the epoxy compound during casting. The plastic sleeve is disposed around the terminal portion in a spaced relationship therewith and in an abutting relation with the pad to provide a barrier to the radial flow of the epoxy compound during casting. Clamping means such as a portable vise is fitted about the conformable pad and is tightened to establish a compressive union at the interface of the conformable pad and the terminal portion of the conductor to prevent leakage. A pair of spring members hold the sleeve in abutting engagement with the surface of the conformable pad during the casting process. In a preferred embodiment, a sealing compound is applied to the interface of the pad and the sleeve and also between the pad and the terminal portion of the conductor to prevent leakage. After the epoxy compound has cured, the clamping means and detachable conformable pad are removed from the assembly and can be reused to encapsulate other conductors.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the stator windings of largedynamoelectric machines such as hydro-generators, and more particularly,to the insulation of the series connected stator coil end turns of suchmachines.

2. Description of the Prior Art

The rating of hydro-generators has been increasing rapidly over the lastfew years. Single-turn coils with Roebel transposition of the conductorstrands are most suited for these larger ratings. The series connectedend turns of this type coil are necessarily large and carry full coilcurrent. These connections may be made by brazing individual strands orgroups of strands from adjacent coils together in a compact manner. Amore convenient method is to braze one or two copper bars betweenadjacent coils.

Such connections in the past have been insulated by means of hand tapingwith an insulating tape. However, because the insulation procedure mustoften be accomplished in the power plant, and because of the limitedaccess to the terminal portions of the series connected coil end turns,the conventional hand taping process is unsuitable. Furthermore, becausethe joints conduct full coil current an insulating structure providingimproved heat transfer is desirable. Of course, a suitable insulationscheme for the brazed structure should be impervious to moisture and oiland should occupy a minimum of space in order to avoid interfering withventilation, and should be suitable for application under fieldconditions with semi-skilled labor.

As an aid to further understanding of the general construction and useof copy encapsulated conductors in dynamoelectric machines, reference ismade to the following examples of the prior art:

1. U.S. Pat. No. 3,151,260, D. C. MacCracken, Jr. et al;

2. U.S. Pat. No. 3,555,316, Donald D. Bleich;

3. U.S. Pat. No. 3,123,729, R. Fagel; and

4. U.S. Pat. No. 2,944,297, J. T. Maynard.

SUMMARY OF THE INVENTION

The invention provides for insulating the terminal portions of statorcoil end turns of a large dynamoelectric machine in a manner whichprovides adequate mechanical reinforcement, effective electricalinsulation, and improved heat transfer as compared with the hand-tapedprior art arrangement. These objects and advantages are realized by amethod and structure for encapsulating the terminal portion of a coilend turn which provides an extremely compact, encapsulated package. Inaccordance with the method of the invention, a detachable conformablepad is secured to a coil end turn terminal portion which is to beencapsulated. The pad includes radially extending side portions whichcircumscribe and extend transversely to the terminal portion of the coilend turn to provide a barrier to axial flow of a liquid pottingcompound. A sleeve member, which may also provided electricalinsulation, is disposed about the terminal portion of the coil end turnin a spaced relationship therewith. The sleeve comprises a continuous,circumferentially extending side portion which is bounded by first andsecond open end portions, the sleeve providing a barrier to the radialflow of the liquid potting compound during casting. The sleeve isdisposed in abutting engagement with the detachable pad to define avolume in combination therewith for receiving the liquid epoxy casting.A liquid potting compound casting material such as epoxy resin havinggood heat transfer properties and good electrical insulation propertieswhen cured is cast into the sleeve until the end turn terminal portionis completely covered to a predetermined depth by the liquid epoxy.After the potting compound is cured to form a hardened mass ofinsulation surrounding the coil end turn portion, the detachable pad isremoved from the assembly.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more fully understood from the following detaileddescription, taken in connection with the accompanying drawings, inwhich:

FIG. 1 is a vertical sectional view of a large hydro-generator havingwinding end turn portions encapsulated by the method of the presentinvention;

FIG. 2 is a fragmentary view of a portion of the stator of the generatorof FIG. 1 taken along the lines II--II;

FIG. 3 is an isometric view of the stator shown in FIG. 2 whichillustrates a brazed connection for the terminal portions of coil endturns which project from the stator core;

FIG. 4 is an enlarged view of a portion of the winding assemblyillustrated in FIG. 3 in which a casting assembly constructed accordingto the teachings of the present invention is shown partially assembled;

FIG. 5 is a view similar to FIG. 4 in which the casting assembly iscompletely assembled;

FIG. 6 is a view similar to FIG. 5 in which the finished encapsulationis illustrated;

FIG. 7A is an isometric view which illustrates the construction of thedetachable, conformable pad shown in FIGS. 5 and 6;

FIG. 7B is an isometric view which illustrates the construction of thesleeve which is shown in FIGS. 5 and 6; and,

FIG. 7C is an isometric view which illustrates the construction of theportable vise and spring members which are shown in FIGS. 5 and 6.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention is shown in FIG. 1 embodied within the stator core of alarge vertical dynamoelectric machine suitable for use as a waterwheeldriven generator. The machine has vertical shaft 10 carrying a rotormember 12 for cooperation with a stator 14 which is supported on afoundation 16 of any suitable type. The shaft 10 and the rotor 12 aresupported on a thrust bearing (not shown) of the usual type and theoverall construction of the machine may be of any usual or desired type.The rotor 12 consists of a spider portion 18 mounted on the shaft 10which may be of any suitable or usual construction. A laminated rim 19is carried on the spider portion 18 and salient poles 20 carrying fieldwindings (not shown) are mounted in the usual manner on the rim 19. Therotor 12 may be of any suitable construction and may be cooled by itsown ventilation system, either separately or in cooperation with that ofthe stator. The machine is shown as being cooled by air flowing axiallythrough the inner polar spaces as indicated by the arrows 21.Ventilating air is circulated through the machine by any desired meanswhich is shown as a centrifugal blower consisting of a plurality ofblades 27 mounted on the rotor. Air flows from the blower in the pathindicated by the arrows 21 and through coolers 29, which may be theusual type, any necessary number of coolers 29 being provided about thecircumference of the machine.

The stator 14 comprises a laminated stator core 24 supported between endplates 25 and a frame 26. The stator core 24 is of laminatedconstruction and is built up of the usual punchings to form acylindrical core having a central bore therethrough with teeth (notshown) extending longitudinally of the bore to form slots 31 betweenthem for the reception of a stator winding 32 of any suitable typeconsisting of a plurality of winding conductors which constitute halfcoils connected at their terminal end portions 34 to form complete coilsand a complete stator winding. The terminal end portions 34 are suitablybraced by a bracing ring 35.

In the illustrative embodiment shown in FIG. 1 and FIG. 2, which istypical of large machines with heavy load currents in the statorwinding, each of the conductors comprising the winding 32 consists oftwo columns of conductor strands (not shown) which are transposed in anydesired manner such as the well-known Roebel transposition. The portionsof the conductors comprising the winding 32 which lie in the slots 31 ofthe stator core 14 are, of course, enclosed in the usual heavy groundinsulation 36 which extends beyond the core almost to the end of theconductors as can be seen in FIG. 2, for example.

As previously described, each of the stator winding conductors 32extends beyond the stator core 14 at each end thereof, and each end ofeach conductor is formed in the usual manner to extend around the coreinto position for connection to the other end of another conductor lyingin a different slot (from slot 31A to slot 31B, for example). Theextreme terminal ends 32A, 32B of each such pair of conductors aredisposed adjacent each other as shown in FIG. 2. The strands of eachconductor are transposed within the slot portion, as previouslydescribed, and are electrically and mechanically joined together attheir terminal end turn portions by means of brazed connections 38. Theterminal portions of the adjacent coils are connected electrically andmechanically to form a series connected coil.

The brazed connection 38 shown in FIG. 3 comprises a pair of brazingbars 38A and 38B which are preferably composed of copper. As previouslyexplained in prior art practice, these terminal coil end turn portionsin some applications are connected by conventional strand joints andthereafter insulated by hand taping. However, according to the teachingsof the present invention, the conductor terminal end portions 32A, 32Bwhich are series connected by the brazed joint 38 are encapsulated in aliquid potting compound 39 (FIG. 6) instead of being hand taped withelectrical insulating tape. The encapsulation provided by the method andstructure of the present invention provides excellent electricalinsulation and heat transfer properties and is physically robust andcompact so that it does not interfere with ventilation and furtherprovides additional mechanical support for the end connections.

The first step in the encapsulation process of the present invention isillustrated in FIG. 4. As there shown, a pad 40 of a conformablematerial such as polyethylene foam is disposed about the projectingterminal portions of the coils 32A and 32B. Other conformable materialssuch as spun glass fiber may be used to good advantage. However, thematerial selected for the conformable pads 40 should be compressible andslightly plastic so that any void which may exist between the pad 40 andthe conductors 32A and 32B will be filled (to prevent leakage of theliquid potting compound 39) by the conformable material of the pad 40when it is compressed about them.

The conformable pad 40 is secured to the terminal portions 32A and 32Bof the winding 32 and includes openings 42 and 44 (FIGS. 4, 7A) whichare prefabricated to provide a close fit between the sides of theconformable pad 40 and the projecting end turn portions. The conformablepad 40 is severed longitudinally along the line 46 so that it may beeasily and quickly fitted around the terminal portions 32A and 32B ofthe winding 32. The conformable pad 40 has radially extending sideportions 47, 49 which circumscribe and extend transversely with respectto the coil end turn terminal portions 32A and 32B to provide a barrierto the flow of the liquid potting compound 39 when it is cast.

A portable vise or clamp 50 is used to provide a compressive force onthe conformable pad 40 to force it into a tight compressive union withthe terminal coil portions 32A and 32B to seal the interface between theterminal coil portions and the pad. The vise or clamps 50 may assume anysuitable construction, and is shown in FIG. 4 as comprising a pair ofjaws or clamping bars 52 and 54 which are connected on either end bymeans of screw bolts 56 and wing nuts 58.

The casting operation is made possible by a sleeve mold 60 which isshown assembled to the conformable pad 40 in FIGS. 5 and 7B of thedrawing. The sleeve 60 comprises a continuous, circumferentiallyextending side portion 62 which is bounded by first and second open endportions 64 and 66. The open end portion 64 of the sleeve 60 is disposedin abutting engagement with the pad 40 with its side portion 62 beingradially spaced from the end terminal portions 32A and 32B and alsobeing radially spaced from the brazed electrical connection 38. Thecombination of the sleeve 60 and the detachable pad 40 provides areceptacle or a mold for containing the liquid potting compound 39 whileit cures. The sleeve 60 is preferably constructed from a dielectricmaterial such as polyester glass to provide electrical insulation forthe end turn conductors.

As discussed above, the portable vise 50 holds the detachableconformable pad 40 in compressive engagement with the end turn terminalportions 32A and 32B to substantially fill any void which may existbetween the terminal portions 32A, 32B and the pad 40 so that leakage ofthe liquid potting compound 39 is prevented.

Also illustrated in FIG. 5 is spring means 70 which holds the sleeve 60against the pad 40 to establish a compressive union at the interface 71of the first open end portion 64 of the sleeve 60 and the conformablepad 40. The spring 70 is shown attached to the second open end portion66 of the sleeve 60 by means of a clip 72 while the opposite end of thespring is shown attached by means of an extension 74 of the spring 70which is curled around the screw bolt 56 of the portable vise 50. Anidentical spring assembly is attached between the vise assembly and thesleeve at the opposite end of the sleeve. Other fastening arrangementswhich are easily assembled and disassembled may be used to goodadvantage.

In some instances, it may be desirable to seal the interface 71 (FIG. 4,FIG. 5) between the sleeve 60 and the conformable pad 40 to preventleakage of the liquid potting compound. Also, it may be desirable toseal the interface 73 (FIGS. 4, 5) between the conformable pad 40 andthe end turn terminal portions 32A and 32B for the same reason. This isaccomplished according to present invention by applying a layer 75 of asealing compound such as butyl rubber to the interface areas 71, 73where additional sealing is desired.

Because it is desirable to remove the conformable pad 40 after thecasting has cured, the exposed surface 76 (FIG. 4) of the pad 40 whichis bounded by the abutting first open end portion 64 of the sleeve 60 istreated with a quick release material 80 which has properties whichinhibit the adhesion of the liquid epoxy casting material 39 to the pad40 so that the pad may be removed without causing its destruction. Thisis accomplished according to the present invention by applying a thinlayer of a release agent 80 (FIG. 4) such as Dow Corning 107 on thesurface of the pad 40 to prevent adhesion of the pad 40 to the lowerportion 82 (FIG. 6) of the cured potting compound 39.

In order to ensure uniform heat transfer from the brazed connection, theliquid potting compound 39 should be distributed about the connectionuniformly. Therefore, it is preferred that the sleeve 60 besubstantially centered about the brazed connection 38 and the terminalend turn portions 32A and 32B. The centering of the sleeve 60 can beaccomplished in most cases manually by simple inspection. However, insome cases, it may be necessary to use some mechanical spacing meansinterposed between the sleeve and the terminal portions to maintain thesleeve in a substantially centered relationship.

A brazed series connection 90 which has been encapsulated according tothe teachings of the present invention is illustrated in FIG. 6 of thedrawings. In a preferred embodiment of the invention, the pottingcompound 39 comprises an easily poured silica-filled epoxy mixture of aapproximately equal parts by weight of silica and resin together with asuitable amount of a curing agent.

The method and apparatus discussed above provides an insulated coil endencapsulated construction which is adequately supported mechanically ina manner to substantially prevent failures caused by vibration andfatigue, the conductor strands being solidly bonded together by thebrazed connection and encapsulated in the hardened epoxy pottingcompound. The sleeve 60 provides effective insulation and is compact sothat it does not interfere with the ventilation of the series connectedend turn portions. The construction is such that it can be appliedquickly and easily by unskilled labor under field conditions. It isespecially suitable for use in winding configurations where access wouldbe too restricted for the use of hand taping as utilized in the priorart. The cast epoxy compound provides both electrical insulation andimproved heat transfer from the brazed series connection as compared tothe conventional hand taped assembly.

While certain preferred materials have been described for the purpose ofillustration, it should be understood that other suitable insulatingmaterials and resins may be used if desired. The particular details ofconstruction shown are, of course, only illustrative and otherequivalent structures may be utilized without departing from the scopeof the invention.

We claim:
 1. In a core member of a dynamoelectric machine having awinding supported by said core, said winding including a plurality ofcoil end turn terminal portions which project from said core, a selectedplurality of said coil end turn terminal portions being disposed inside-by-side relation with respect to one another for connection inelectrical series relation one to another by electrical connectingmeans, the combination with said winding of a casting assembly forencapsulating said end turn terminal portions and electrical connectingmeans, said casting assembly comprising:a removable pad of conformablematerial secured to said selected end turn terminal portions, said padhaving radially extending side portions which circumscribe and extendtransversely to said selected coil terminal portions to provide abarrier to the axial flow of a fluid relative to said selected terminalportions; a sleeve disposed around said selected end turn terminalportions in a spaced relation therewith and in an abutting relation withsaid pad, said sleeve having a continuous, circumferentially extendingside portion bounded by first and second open end portions, said sleeveproviding a barrier to the radial flow of a fluid relative to said endturn terminal portion, said first open end portion of said sleeve beingdisposed in abutting engagement with said pad, and said side portionbeing radially spaced from said end turn terminal portions; meanscompressing said removable pad against said end turn terminal portionsto substantially fill a void which may exist between said coil end turnterminal portion and said pad; means forcing said sleeve against saidpad to establish a compressive union at the interface of said first openend portion of said sleeve and said conformable pad; and, a compounddisposed in the volume defined by the union of said sleeve and said pad,said compound when cured providing electrical insulation and thermalconduction for said end turn terminal portions and said electricalconnecting means.
 2. The combination defined in claim 1, including afirst layer of sealing compound disposed intermediate said pad and saidfirst open end portion of said sleeve, and a second layer of sealingcompound disposed intermediate said pad and said selected coil end turnterminal portions.
 3. The combination defined in claim 1, including alayer of material having properties which inhibit the adhesion of saidliquid insulating material to said pad disposed on the interior surfacearea of said pad bounded by the abutting first open end portion of saidsleeve.